Rectifying system



March 19, 1935. E. KERN RECTIFYING SYSTEM 2 Sheets-Sheet 1 Filed Nov.28, 1932 MAO/M E. KERN RECTIFYING SYSTEM March 19, 1935.

Filed Nov. 28, 1932 2 Sheets-Sheet 2 Patented Mar. 19, 1935 UNITEDSTATES PATENT OFFICE RECTIFYING SYSTEM Switzerland Application November28, 1932, Serial No. 644,598 In Germany December 28, 1931 14 Claims.

This invention relates to improvements in regulating systems and moreparticularly to means for regulating the output of a rectifying systememploying an electron discharge device in which the flow of current iscontrolled by energization of suitable control electrodes.

In rectifying systems employing an electron discharge device, thevoltage of the direct current output circuit is primarily a function ofthe voltage of the alternating current supply line but also varies independence on the current delivered by the system to the currentconsuming devices therein in the usual rectifying systems, the voltageof the direct current output circuit decreases when the current withinsuch circuit increases. It is however frequently desired to obtainconstant output voltages at all loads or to obtain variations of theoutput voltage which are different from the variations inherentlyproduced by a rectifying system. Any desired relation between the valuesof voltage and of current in the output circuit may be automaticallyobtained by controlling the energization of the control electrodes ofthe discharge device by means of a distributor operable at the frequencyof the supply line voltage and by adjusting such distributor dependingupon conditions within the system.

It is, therefore, among the objects of the present invention to providea regulating system for a rectifying system employing an electrondischarge device whereby the output voltage of the rectifying system isautomatically regulated in dependence upon conditions within thecircuits comprising such system.

Another object of the present invention is to provide a regulatingsystem for a rectifying system employing an electron discharge devicewhereby the control electrodes of the device is energized through adistributor which is automatically adjusted in dependence uponconditions within the rectifying system.

Another object of the present invention is to provide a regulatingsystem for a rectifying system employing an electron discharge device inwhich the magnetic axis of an auxiliary synchronous motor isautomatically shifted in dependence upon conditions within therectifying system to adjust the energization of the control electrodesof the device and to regulate the output voltage of the system.

Objects and advantages, other than those above set forth, will beapparent from the following description when read in connection withaccompanying drawings, in which:

Fig. 1 diagrammatically illustrates one embodiment of the presentinvention in which the output voltage of an electron discharge deviceoperable as an alternating current rectifier is regulated by energizingthe control electrodes of the device through a distributor havingdriving means automatically adjusted by means of a regulator responsiveto the magnitudes of the voltage and of the current in the outputcircuit,

Fig. 2 diagrammatically illustrates a portion of a modified embodimentof the present invert-- tion differing from the embodiment illustratedin Fig. 1 in that the distributor is directly adjusted depending uponthe value of only the current in the output circuit;

Fig. 3 diagrammatically illustrates another modified embodiment of thepresent invention differing from the embodiment illustrated in Fig. 2 inthat the distributor is adjusted depending upon the value of the currentin the input circuit; and

Fig. 4 diagrammatically illustrates a further modified embodiment of thepresent invention differing from the embodiment illustrated in Fig. 3 inthe means for adjusting the distributor driving means.

Referring more particularly to the drawings by characters of reference,reference numeral 6 designates an alternating current supplyline of anydesired number of phases and at any desired frequency, being hereinshown as a three-phase line for the-reason that such type of line ismost frequently utilized in practice. Line 6 energizes the deltaconnected primary winding 7 of a supply transformer having a secondarywinding 8 comprising a plurality of winding portions connected in starto form a neutral point. The different portions of winding 8 areseverally connected with the anodes 9 of an electron discharge device 11herein shown as being operable as an alternating current rectifier.Rectifier 11 is herein illustrated as being of the vapor type having avaporizable cathode 12 and is assumed to be provided with the usualignition and excitation means (not shown in Figs. 1, 2 or 3). Cathode 12is connected with the positive conductor 13 of the output circuit havingthe negative conductor 14 thereof connected with the neutral point ofwinding 8.

Rectifier 11 is provided with control electrodes 16 which may have anegative potential with respect to the potential of cathode 12 impressedthereon by means of a direct current generator 19 through resistances 17and 18. A resistance 21 having a mid-tap connected with conductor 13 isconnected across the terminals of the generator 19 to permit generator19 to deliver current at voltages both positive and negative withrespect to cathode l2. Generator 19 is preferably driven by means of asynchronous motor 22 having an armature 23 energized from line 6 and aplurality of field windings 24, 25 and 26 spatially distributed over thefield of the motor. Motor 22 also drives the brush of a distributor 2'7through which the control electrodes may be sequentially energized at apositive potential with respect to the potential of cathode 12 fromgenerator 19 over resistance 17. Winding 26 of motor 22 is connected inseries with a circuit comprising windings 24 and 25 connected inparallel and interconnected through resistances 28 of a. regulator 29.Such circuit maybe energized from any suitable direct current source andis preferably energized from generator 19. Regulator 29 may be of anytype known in the art and is preferably operated by means of a voltagecoil 31 connected across direct current line 13, 14 through a rheostat34 and by means of a current coil 32 connected across a shunt 33 andenergized from point of connection of resistance 28 with generperipheryof the field of the motor.

ator 19 to regulate the distribution of current between windings 24 and25. It will be understood that, with suitable modifications, the controlelements described may be utilized for controlling a discharge deviceoperable for any operation known in the art such as direct currentinversion, frequency conversion, etc.

In operation, assuming the system to be connected as shown in Fig. l andline 6 to be energized, winding 7 receives current from line 6 with theresult that winding 8 impresses sixphase alternating current voltages insequence on the anodes 9 of rectifier 11. The control electrodes 16 ofrectifier 11 are generally maintained at a negative potential withrespect to cathode 12 from. generator 19 over resistances 1'7 and 18 toprevent the operation of the anodes associated therewith. When an anode9 is at a positive potential with respect to cathode 12, the associatedcontrol electrode 16 receives a positive potential from generator 19over one of the segments of distributor 2'7 and resistance 17. Upon suchpositive energization of control electrode 16, anode 9 carries current,the flow of such current continuing until anode 9 is no longer positive.

with respect to cathode 12. Such cycle of operation is sequentiallyrepeated for each anode of rectifier 11 during each cycle of the voltageof line 6, with the result that the system supplies a substantiallyuniform direct current to the output circuit 13, 14. As is well known,the voltageof the output circuit may be regulated by adjusting themoment in the voltage cycle of line 6 at which each control electrode ispositively energized through distributor 2'7.

When the load" connected with circuit 13, 14 changes, the current drawnfrom the system also changes thereby causing a change in the currentflowing in coil32. Due to the inherent characteristics of the rectifyingsystem, the voltage of the output circuit also changes thereby causing achange in the potential in coil 31. Regulator- 29 therefore changes itsposition to shift the connection of generator 19 with resistance 28. Therelative amounts of current flowing through windings 2.4 and 25 aretherefore changed thus causing a spatial shift of the magnetic fluxalong the The magnetic axis of the field being thus shifted, the rotorof motor 22; will continue to rotate at synchronous s eed but, at anyinstant, will be in a position, with respect to the voltage wave of line6, which is difierent from the position of such rotor at the previousload value. The brush of distributor 2'? therefore comes'into contactwith each segment of the distributor at a time, considered with respectto the voltage wave of line 6, which is different from the time at whichsuch contact occurred previously. Each control electrode thereforepermits the associated anode to operate during a different period of thevoltage wave of line 6 thus causing the voltage of line 13, 14 toreach avalue differing from the value which such voltage would have in theabsence of regulator 29. By suitably choosing the characteristics ofregulator 29, the regulation between the current and the voltage in line13, 14 may be predetermined in any desired manner; in particular, suchvoltage may be maintained constant at all loads or may be made toincrease at increasing values of current. Such relation may be modifiedby changing the adjustment of rheostat 34. v

In the embodiment illustrated in Fig. 2, regulator 29 is omitted andwindings 24 and 25 are connected in series across shunt 33. Windings 24and 26 are then connected in series and are supplied from generator 19through a rheostat 36. The negative terminal of generator 19 isconnected with conductor 13 on the cathode side. of shunt 33 so that thepositive terminal of the generator may be utilized for positivelyenergizing the brush of distributor 2'7 with respect to the potential ofthe cathode 12. The control electrodes may be negatively energized withrespect to cathode 12 by means of a suitable sourceof direct current andare preferably energized through a voltage divider 38 connected acrossline 13, 14.

The operation of the rectifying system to which the present embodimentis applied, is similar to that of the rectifying system illustrated inFig. 1.

When the current in line 13, 14 changes, the voltage drop across shunt33 changes thereby changing the amount of current flowing throughwindings 25 and 24. As in the'embodiment illustrated in Fig. 1, suchchange in the currents of such windings causes a shift of the magneticaxis of the field of motor 22 resulting in a change in the position ofthe brush of distributor 27, relative to the position of the segmentsthereof, such as to regulate the output voltage of the rectifyingsystem. In the present embodiment the relation between the voltage andthe current in the output circuit may be modified by adjustment ofrheostat 36 controlling the how of current in windings 24 and 26.

In the embodiment illustrated in Fig. 3', the current flowing throughwindings 24 and 25 is obtained from a current transformer 39 energizedby the input current of one terminal of transformer '7, 8. The secondarywinding of transformer 39 supplies windings 24 and 25 through a rheostat41 and through a current rectifier 42 of any desired type. The terminalsof the secondary winding of transformer 39 may be bridged by tworeactors 43 and 44 having the windings thereof connected in series. Thecores of reactors 43' and 44 may be or" different cross sections sothat, upon energization of the windings of the reactors, the core ofreactor 43 will become saturated for a value of current at which thecore of reactor 44 is still magnetized below the saturation point.

The operation of the rectifying system of the present embodiment issimilar to that of the system illustrated in Fig. 1. When the current inline 13, 14 increases, the current drawn from line 6 by transformer "I,8 increases correspondingly thus causing an increasing current to flowin the secondary winding of current transformer 39. A portion of suchcurrent ficwsover rheostat 41 and rectifier 42 into windings 24' and 25thereby causing a shift of the magnetic axis of motor 22 in a mannersimilar to that previously described. The amount of current flowingthrough the windings of reactors 43 and 44 increases substantiallyproportionately to the current drawn by winding 7 until the core ofreactor 43 becomes saturated. The relation between the current intransformer 39 and the current drawn by the reactors 43 and 44 changesso that, at currents increasing above the previous value, the effect ofthe current of transformer 39 on the position of the field of motor 22will be different from that obtained at lower currents. The voltage ofline 13, 14 may thus be regulated to present variations which are nolonger continuous, but which may present any desired irregularities. Itwill be understood that the voltage of line 13, 14 may be made to followa number of separate relations for different ranges of values of theoutput current by employing a larger number of reactors having coressaturable at different values of current. The value of the outputvoltage may also be varied by adjustment of rheostat 41.

In the embodiment illustrated in Fig. 4, motor 22 is shown as beingprovided with a six-phase armature 46 and with a single field winding4'7. Winding 47 is energized from the excitation circuit of rectifier11, such circuit comprising a transformer 48 energized from line 6 andsupplying two excitation anodes 49 and 51 through resistances 52 and 53,the resistance 54 and a reactor 56. The excitation current flowingthrough resistance 54 is av substantially uniform direct current due tothe presence of reactor 56 and energizes the field winding of motor 22similarly to the energization thereof by generator 19 in the previouslydescribed embodiments. Three of the windings of armature 46 areenergized from line 6 as in the previously described embodiments and theother three windings are energized from current transformers 57, 58 and59 connected in the circuit of winding 7. The currents in the lastmentioned armature windings may be regulated by means of rheostats 61,62 and 63 connected across the terminals of the secondary windings oftransformers 57, 58 and 59. The common point of resistance 54 and ofreactor 56 is maintained at a substantially uniform direct currentnegative potential with respect to the potential of the cathode 12 dueto the flow of excitation current in resistance 54 and such point istherefore connected with the control electrodes of rectifier 11 toenergize such control electrodes at a negative potential. Such controlelectrodes are then energized at a positive potential through the brushof distributor 2'7 from any suitable source of direct current such as abattery 64.

The operation of the rectifying system shown in the present embodimentis similar to that of the system illustrated in Fig. 1. When the currentin the output circuit increases, the current drawn by winding 7 fromline 6 increases correspondingly and transformers '7, 58 and 59 willcause a shift of the position of the rotating magnetic field in armature46 with respect to the voltage cycle in supply line 6. The shift of themagnetic axis of armature 46 thus obtained causes the rotor of motor 22to continue rotating at synchronous speed but such rotor will, at everyinstant, have a position, with respect to the voltage cycle of line 6,which is different from the position it had previously. Adjustment ofthe position of the brush of distributor 2'7 with respect to the voltagecycle of line 6 is thus obtained as in the previously describedembodiments to regulate the voltage of line 13,

14. In the present embodiment, the voltage applied to motor 22 may beadjusted by adjustment of the rheostats 61, 62 and 63 whereby anydesired fraction of the currents supplied by transformers 5'7, 58 and 59may be supplied to the windings of armature 46.

Although but a few embodiments of the present invention have beenillustrated and described, it will be apparent to those skilled in theart that various changes and modifications may be made therein withoutdeparting rom the spirit of the invention or from the scope of theappended claims.

It is claimed and desired to secure by Letters Patent:

1. In an electric current rectifying system, an alternating currentsupply line, an electron discharge device having anodes with associatedcontrol electrodes and a cathode, a transformer connecting said supplyline with the anodes of said device, a direct current output line, oneof the conductors of said output line being connected with the cathodeof said device and the other conductor thereof being connected with saidtransformer, a direct current generator for continuously applying anegative potential relative to the potential of the cathode on thecontrol electrodes of said device, means for connecting said generatorintermittently with the control electrodes to apply a potential theretopositive relative to the potential of the cathode of said device, andmeans operable responsive to variations in conditions of said system forvarying the operation of the first said means.

2. In an electric current rectifying system, an I alternating currentsupply line, an electron discharge device having anodes with associatedcontrol electrodes and a cathode, a transformer connecting said supplyline with the anodes of said device, a direct current output line, oneof the 1 conductors of said output line being connected with the cathodeof said device and the other conductor thereof being connected with saidtransformer, means for continuously impressing a negative potentialrelative to the potential of the cathode on the control electrodes ofsaid device, means for sequentially impressing a potential impulsepositive relative to the cathode on the control electrodes of saiddevice, a motor operable at synchronous speed relative to the voltagecycle of said supply line for operating both said means, and means forshifting the magnetic axis of said motor in response to conditions insaid direct current line.

3. In an electric current rectifying system, an alternating currentsupply line, an electron discharge device having anodes with associatedcontrol electrodes and a cathode, a transformer connecting said supplyline with the anodes of said device, a direct current output line, oneof the conductors of said output line being connected with the cathodeof said device and the other conductor thereof being connected with saidtransformer, a direct current generator for continuously applying anegative potential relative to the potential of the cathode on thecontrol electrodes of said device, means connecting said generatorintermittently with the control electrodes to apply a potential theretopositive relative to the potential of the cathode of said de vice, amotor operable at synchronous speed relative to the voltage cycle ofsaid supply line for operating said generator and said means, and

means for shifting the magnetic axis of said motor in response toconditions in said rent line.

i. In an electric current rectifying system, an alternating currentsupply line, an electron discharge device having anodes with associatedcontrol electrodes and a cathode, a transformer connecting said supplyline with the anodes of said device, a direct current output line, oneof the conductors of said output line being connected with the cathodeof said device and the other conductor thereof being connected with saidtransformer, means for continuously impressing a negative potentialrelative to the potential of the cathode on the control electrodes ofsaid device, means for sequentially impressing a potential impulsepositive relative to the potential of the cathode on the controlelectrodes of said device, a motor operable at synchronous speedrelative to the voltage frequency of said supply line connected tooperate both said means and having a plurality of field excitationwindings, and means responsive to current and voltage conditions in saiddirect current line to control energization of the field windings ofsaid motor.

5. In an electric current rectifying system, an alternating currentsupply line, an electron discharge device having anodes with associatedcontrol electrodes and a cathode, a transformer connecting said supplyline with the anodes of said device, a direct current output line, oneof the conductors of said output line being connected with the cathodeof said device and the other conductor thereof being connected with saidtransformer, means for continuously impressing a negative potentialrelative to the potential of the cathode on the control electrodes ofsaid device, means for sequentially impressing a potential impulsepositive relative to the potential of the cathode on the controlelectrodes of said device, a motor operable at synchronous speedrelative to the voltage frequency of said supply line connected tooperate both said means and having a plurality of field excitationwindings, a resistance connected with the field windings of said motor,and a regulator having a current coil anda potential coil connected withsaid direct current'line and varying the amount of said redirectcursistance connected in circuit with the field windings of said motorto control energization thereof. 6. In an electric current rectifyingsystem, an alternating current supply line, an electron discharge devicehaving anodes with associated control electrodes and a cathode, atransformer connecting said supply line with the anodes of said device,a direct current output line, one of the conductors of said output linebeing connected with the cathode of said device and the other conductorthereof. being connected with said transformer, a direct currentgenerator, a resistance connected with the terminals of said gen erator,a point of said resistance being connected with one of the conductors ofsaid direct current line, one of the terminals of said resistance beingconnected with the control electrodes to continuously impress thereon apotential negative relative to the potential of the cathode of saiddevice, means for sequentially connecting the other terminal of saidresistance with the control electrodes to impress thereon a potentialimpulse positive relative to the potential of the cathode of saiddevice, and means operable responsive to variations in conditions in thesystem for varying the operation of the first said means.

7. In an electric current rectifying system, an alternating currentsupply line, an electron dis-- charge device having anodes withassociated control electrodes and a cathode, a transformer connectingsaid supply line with theanodes of said device, a direct current outputline, one of the conductors of said output line being connected with thecathode of said device and. the other conductor thereof being connectedwith said transformer, a direct current generator, a resistanceconnected with the terminals of said generator, a point of saidresistance being connected with one of the conductors of said directcurrent line, one of the terminals of said resistance being connectedwith the control electrodes to continuously impress thereon a potentialnegative relative to the potential of the cathode of said device, meansfor sequentially connecting the other terminal of said resistance withthe control electrodes to impress thereon a potential impulse positiverelative to the potential of the cathode of said device, a motoroperable at synchronous speed relative to the voltage frequency of saidsupply line for operating said generator and said means, and meansoperable in response to changes in conditions in said direct currentline for shifting the magnetic axis of said motor.

8. In an electric current rectifying system, an alternating currentsupply line, an electron discharge device having anodes with associatedcon- 'rol electrodes and a cathode, a transformer connecting said supplyline with the anodes of said device, a direct current output line, oneof the com ductors of said output line being connected with the cathodeof said device and the other conductor thereof being connected with saidtransformer, a' direct current generator, a resistance connected withthe terminals of said generator, a point of said resistance beingconnected with one of the conductors of said direct current line, one ofthe terminals of said resistance being connected with the controlelectrodes to continuously impress thereon a potential negative relativeto the po tential of the cathode of said device, means for sequentiallyconnecting the otherterrninal of said resistance with the controlelectrodes to impress thereon a potential impulse positive relative tothe potential of the cathode of said device, a motor operable atsynchronous speed relative to the voltage frequency of said supply lineconnected to operate both said generator and said means and having aplurality of field excitation windings, a resistance connected with thefield windings of said motor, and a regulator having a current coil anda potential coil connected with said direct current line operable tovary the amount of said resistance connected in circuit with the fieldwindings of said motor to control energization thereof.

9. In an electric current rectifying system, an alternating currentsupply line, an electron discharge device having anodes with associatedcontrol electrodes and a cathode, a transformer connecting said supplyline with the anodes of said device, a direct current output line, oneof the conductors of said output line being connected with the cathodeof said device and the other conductor thereof being connected with saidtransformer, a resistance connecting the conductors of said output line,a point of said resistance being connected with the control electrodesto continuously impress thereon a negative potential relative to thepotential of the cathode of said device, means for sequentiallyimpressing a potential impulse positive relative to the potential of thecathode on the control electrodes of said device, a motor operable atsynchronous speed relative to the voltage frequency of said supply linefor up crating said means, and means operable responsive to changes insaid direct current line for shifting the magnetic axis of said motor.

10. In an electric current rectifying system, an alternating currentsupply line, an electron discharge device having anodes with associatedcontrol electrodes and a cathode, a transformer connecting said supplyline with the anodes of said device, a direct current output line, oneof the conductors of said output line being connected with the cathodeof said device and the other conductor thereof being connected with saidtransformer, a resistance connecting the conductors of said output line,a point of said resistance being connected with the control electrodesto continuously impress thereon a negative potential relative to thepotential of the cathode of said device, a direct current generatorarranged to be connected with the control electrodes to impress thereona potential impulse positive reative to the potential of the cathode ofsaid device, means for sequentially connecting said generator with thecontrol electrodes of said device, and a motor operable at synchronousspeed relative to the voltage frequency of said supply line foroperating said generator and said means, said motor having a pluralityof field windings connected with and energized from one conductor ofsaid direct current line responsive to current flow therein to shift themagnetic axis of said motor to vary operation of said generator and saidmeans.

11. In an electric current rectifying system, an alternating currentsupply line, an electron discharge device having anodes with associatedcontrol electrodes and a cathode, a transformer connecting said supplyline with the anodes of said device, a direct current output line, oneof the conductors of said output line being connected with the cathodeof said device and the other conductor thereof being connected with saidtransformer, a direct current generator, a resistance connected with theterminals of said generator, a point of said resistance being connectedwith one of the conductors of said direct current line, one of theterminals of said resistance being connected with the control elect esto continuously impress thereon a potei negative relative to thepotential of the cathode of said device, means for sequentiallyconnecting the other terminal of said resistance with the controlelectrodes to impress thereon a potential impulse positive relative tothe potential of the cathode of said device, a motor operable atsynchronous speed relative to the voltage frequency of said supply lineand arranged to operate said generator and said means and having aplurality of field excitation windings, and means associated with saidtransformer and responsive to conditions therein for varying the currentdistribution in the field windings of said motor to control energizationof the control electrodes of said device.

12. In an electric current rectifying system, an alternating currentsupply line, an electron discharge device having anodes with associatedcontrol electrodes and a cathode, a transformer connecting said supplyline with the anodes of said device, a direct current output line, oneof the conductors of said output line being connected with the cathodeof said device and the other conductor thereof being connected with saidtransformer, a direct current generator, a resistance connected with theterminals of said generator, a point of said resistance being connectedwith one of the conductors of said direct current line, one of theterminals of said resistance being connected with the control electrodesto continuously impress thereon a potential negative relative to thepotential of the cathode of said device, means for sequentiallyconnecting the other terminal of said resistance with the con-- trolelectrodes to impress thereon a potential impulse positive relative tothe potential of the cathode of said device, a motor operable atsynchronous speed relative to the voltage frequency of said supply linearranged to operate said generator and said means and having a pluralityof field excitation windings, a current transformer associated with thefirst said transformer, reactors connected with said currenttransformer, and an electric current rectifier connecting said reactorswith the field windings of said motor operable responsive to changes inconditions in the first said transformer for shifting the magnetic axisof said motor.

13. The combination of direct and alternating current circuits, anelectron discharge device having electrodes connected with and formingasymmetric conductors for the fiow of current through said device fromone to the other of said circiuts, a control electrode for controllinginitiation of said flow of current between said circuits by way of saidconductors, means having connection with said control electrode forimpressing potential thereon of such sign and magnitude as to preventinitiation of flow of current between said conductors, means havingconnections for intermittently impressing potential on said controlelectrodes of such sign and magnitude as to perinitiation of fiow ofcurrent between said circuits by way of said conductors, motor meansoperable at synchronous speed relative to the voltage frequency of saidalternating current circuit and comprising a plurality of fieldexcitation windings for operating the second said means, a source ofcurrent for energizing said windings, and means operable responsive toand in dependence upon changes in conditions in one of said circuits forvarying the flow of current through the respective said windings tothereby shift the magnetic axis of said motor to vary th operation ofthe second said means.

14. The combination of direct and alternating current circuits, anelectric current converting device having a cathode and a plurality ofanodes interconnecting said circuits, a plurality of control electrodesseverally associated with said anodes, means having connections forcontinuously impressing potential on said control electrodes of suchsign and magnitude as to prevent initiation of flow of current betweensaid circuits by way of said anodes and cathode, means havingconnections for intermittently and sequentially impressing potential onsaid control electrodes of such sign and magnitude and during suchrecurring periods as to permit flow of current between said circuits byway of the associated anodes, motor means operable at synchronous speedrelative to the voltage cycle of said alternating current circuit andcomprising a plurality of windings foropcrating the second said means, asource of current for energizing said windings, and means operableresponsive to and in dependence upon changes in conditions in one ofsaid circuits for varying the fiow of current through the respectivesaid windings to thereby shift the magnetic axis of said motor to varythe operation of the second said means.

ERWIN KERN.

